John Cleves Symmes Jr. was an American soldier, trader, and lecturer, who proposed a theory of the hollow Earth. According to his idea, our planet consists of five concentric spheres, with our outer Earth and its atmosphere as the largest. The poles of the Earth serve as the openings to the inner lands and a source of the sunlight, which gets reflected on every of the lover spheres inside the Earth to make life there possible. Symmes never had time to write down his ideas. As one of his devoted students, James McBride collected the materials of Symme's lectures and the work of the Swiss mathematician Leonhard Euler to present a scientific account of the theory of concentric spheres.